Prepare the grill for direct cooking over medium heat (350° to 450°F).
In a small bowl combine the topping ingredients and blend with a fork.
Brush the cooking grates clean. Grill the mussels over direct medium heat, with the lid closed, until they open, 2 to 5 minutes. Transfer the mussels to a plate. Discard any mussels that have not opened. Preheat the grill pan over direct medium heat for about 10 minutes.
When the mussels are cool enough to handle, pull away the top shell, leaving the mussel in the bottom half of the shell. Spoon 1 teaspoon of the topping on top of each mussel.
Place the mussels in a single layer on the grill pan. Grill over direct medium heat, with the lid closed, until the topping is bubbling, 2 to 5 minutes. Remove from the grill and top with the parsley. Serve immediately.